1. Field of the Invention
The present invention relates to a lens barrel having a moving barrel and a cam mechanism for driving the moving barrel to move in the optical axis direction.
2. Description of the Related Art
A zoom lens in which a moving barrel (first barrel) is guided along an optical axis without rotating thereabout relative to another barrel (second barrel) is well known. The zoom lens is driven to move along the optical axis by a cam mechanism including a cam ring arranged concentrically to the first barrel. The cam ring is provided with a plurality of cam slots in which a corresponding plurality of followers are respectively fitted, so that the first barrel moves along the optical axis relative to the second barrel when the cam ring rotates about the optical axis relative to the first barrel.
In such a conventional zoom lens there is a possibility of the followers running off the cam slots if the moving barrel is forced to move along the optical axis by a strong external force, in the case where the lead of the cam slots is large, i.e., where the cam slots are formed such that the moving barrel moves by a large distance along the optical axis for an amount of rotation of the moving barrel relative to the second barrel; particularly in the case where the amount of engagement of each of the followers with the corresponding cam slot is small. Therefore, in a conventional zoom lens having such a structure in which the amount of engagement of each of the followers with the corresponding cam slot is small, the strength of the cam mechanism is insufficient while there is excessive play in the cam mechanism.